Many bio-molecules absorb light in the UV range and fluoresce under the beam of a laser. Because of this attribute, UV optical lasers can be used in analytical devices for the biotechnology, pharmaceutical, and medical markets, solid state white lighting, sterilization and disinfectant devices, and water purification systems. It has been a longstanding goal to shrink the large and expensive lasers that are currently used in bio-agent detection systems.
The wavelength range of 337.5 nanometers (nm) to 450 nm (hereinafter the “wavelength range”) is of interest in the field of spectroscopy for the detection of proteins such as tryptophan, Nicotinamide Adenine Dinucleotide (NADH) and flavin compounds. However, there exists a lack of selectable wavelength laser sources for emitting light in this wavelength range. Note that a “selectable wavelength laser” refers to a laser for which the user can select the wavelength of the emission during the manufacturing process.
Indium Gallium Nitride (InGaN) lasers and Aluminum Gallium Nitride (AlGaN) lasers are capable of emitting continuous and pulsed light in this wavelength range. However, InGaN/AlGaN lasers are costly to produce.
Previously, emerald lasers have been made and used at the wavelength of 765 nm. However, the application of such lasers has historically been hampered by the need for large, high quality crystals that are slowly grown by a hydrothermal method and pumped by high power flash lamps.
An example of an emerald laser is disclosed in “CW Laser pumped Emerald Laser,” by Shand, et al, IEEE Journal of Quantum Electronics, Vol. QE-20, No. 2, February 1984, wherein a continuous wave (CW) laser pumped emerald laser is described using an emerald sample having a 2.8 mm length and 3.8×5.1 mm cross section with 1.8 atm percent Cr pumped longitudinally by a CW laser at 647.1 nm. The fraction of pump photons converted into laser photons, or quantum efficiency was 69 percent, which the author attributed to optical loses in the cavity. The output laser wavelength was 765 nm and was polarized parallel to the 5.1 mm sample edge, which contained a projection of the c-axis. The observed tuning range of the emerald laser was reported as 728.8-809.0 nm, which did not cover the entire fluorescence range of emerald (700-850 nm), a fact that the author attributed to the excited state absorption of the laser photons. Another publication entitled “A Tunable Emerald Laser,” by Shand, et al., IEEE Journal of Quantum Electronics, Vol. QE-18, No. 11, February 1982, discloses a laser oscillator made with a 19×4 mm diameter rod, with the c axis at approximately 45 degrees to the rod axes. The optical cavity was formed with a high reflector and a 95 percent reflectivity output coupler. The described laser was reported as having emitted 6.8 mJ at 757.4 nm. The laser had large loses (approximately =0.11 cm−1), presumably due to the beam breakup which was attributed to planes in the crystal having slightly different indexes of refraction. In the article entitled “Highly Efficient Emerald Laser,” by Lai, Journal of the Optical Society of America, B, Vol. 4, No. 8, August 1987, an emerald laser is described with peak-emission cross section of 3.1×10−20 cm2 at room temperature. A 76% laser quantum yield was measured with lasing at 768 nm.
In the past, efforts have been made to provide for doubling crystals. For example, U.S. Pat. No. 4,982,405 to Zayhowski, et al., which is hereby incorporated by reference.
Efforts have also been made to provide semiconductor-laser-pumped solid state lasers, with an increased focus towards miniaturization, increasing the output power and improving beam quality. An example of a laser diode pumped solid state laser is shown, for example, in U.S. Pat. No. 6,341,1390 to Baer, et al., hereby incorporated by reference, Baer, et al., discloses the use of a neodymium or other rare earth doped solid state (RE:solid) laser which is pumped by a matched high efficiency laser diode. The intra-cavity frequency doubled RE:solid assembly of Baer, et al., produces a laser beam output in the visible spectrum near infrared. A further example of a laser pumped solid state laser is shown in U.S. Pat. No. 6,341,139 to Ohtsuka, et al., hereby incorporated by reference, wherein a semiconductor-laser-pumped solid state laser includes a solid state laser medium doped with a rare earth element such as neodymium and a semiconductor laser which emits a pumping laser beam for pumping the solid state laser medium.